The invention relates generally to data communications and more particularly to high speed telecommunications over a twisted pair connection.
The sudden popularity of the Internet and other similar wide area communications platforms has led to an intense push for higher data transmission rates over twisted pair wiring. Most residential Internet users access the Internet through a local Internet Service Provider (ISP). The service provider communicates with subscribers over the Public Switched Telephone Network (PSTN). Since most users access the Internet through a twisted pair As a result, the demand for increased data transmission rates over analog twisted pair wiring is at an all time high. The most recent widespread standard is xe2x80x9c56Kxe2x80x9d analog modem technology developed by U.S. Robotics and Rockwell/Lucent. While these technologies will not generate true 56 kbps performance under typical subscriber line conditions, they do provide a boost in performance from the previous standard of bidirectional 33.6 kbps.
Theoretically, a connection of 64 kbps should be attainable between the subscriber and the Internet Service Provider (ISP) via a standard Plain Old Telephone Service (POTS) connection. This is because 64 kbps is the rate at which data is transferred from the central office linecard to the ISP or other remote terminal. Several factors prevent this from happening including imperfect line conditions and varying local loop lengths common to POTS analog networks. The primary reason, however, for this less than the theoretical transmission rate is that the PSTN was designed to carry voiceband frequencies in the range of 300-3.4 KHZ.
Communications protocols such as Asymmetric Digital Subscriber Lines (ADSL) have been developed to increase the effective bandwidth of existing twisted pair wiring. Ideally, such communications protocols would allow both voice and data communications capabilities over the same twisted pair connection. This eliminates the need to develop a new infrastructure to accommodate increased transmission rates and provides a feasible solution for increased data transmissions for the near future.
A problem associated with using the same twisted pair connection to carry both voice and data signals is that the PSTN limits the useful spectrum of the data signal component. Most POTS devices assume that signals above the 3.4 kHz point contain too much noise for reliable clear voice communications. On the other hand, advances in digital signal processing now permit the resolution of signals past the 3.4 kHz barrier for reliable digital communications. In addition, improved modulation schemes and error correction protocols permit recovery of the underlying digital data contained in the analog carrier.
The invention overcomes the limitation in bandwidth of twisted pair connection between the user and the linecard at the central office facility (CO) by permitting increased downstream and upstream rates using an analog modem communicating over the PSTN.
According to one embodiment, a communications device with an extended Plain Old Telephone Service (xe2x80x9cPOTSxe2x80x9d) filter is disclosed that provides more bandwidth for V.34, V.90 and other data communications protocols. The device comprises an analog interface coupled for coupling to a PSTN twisted pair connection and having a variable bandwidth analog filter; a digital interface couples the device to a digital backplane; a signal conversion circuit is interspersed between the analog interface and the digital interface; a control circuit is operably coupled to the filter and configured to adjust its roll-off point depending on the connection type between a user and the central office. For example, in a data connection, the control circuit can extend the frequency roll-off point of the filter to 3.8 kHz permitting the use of more bandwidth than is achieved in a typical POTS connection.
According to another embodiment, the communications device can be utilized as a central office linecard with a variable frequency filter with a roll-off point at 3.8 kHz and 14 dB attenuation at 4 kHz. During standard voice communications, the roll-off point of the filter is 3.4 kHz corresponding to a POTS band.
According to another embodiment, the same general purpose architecture of the linecard device with an extended roll-off is employed in a modem suitable for use by the subscriber. The modem employs an analog interface to a twisted pair connection coupling the subscriber to their local central office for data communications. The modem can accommodate multiple modulation and/or transmission protocols such as V.34, V.34+ and/or V.90. When a central office linecard with a variable frequency filter is provided in the central office facility, the modem allows increased data mode communications using bandwidth outside the traditional POTS spectrum.
Since the A/D and Digital to Analog (D/A) components can withstand lower signal-to-noise ratios, increased transmission is realized by extending the filters to 3.8 KHz or 4.0 kHz, approximately.
According to still another embodiment, the linecard incorporates a line monitoring mechanism that enable the linecard to determine when a data connection has been initiated. The line monitoring mechanism monitors the Pulse Code Modulated (PCM) data received from the interface to the service provider on the digital backplane. A certain amount of intelligence is employed in the line monitoring mechanism to cause the variable frequency filter to extend when a data connection has been initiated.
A technical advantage of the invention is that it provides the user with increased bandwidth over the same twisted pair connection used for POTS.
Another technical advantage of the invention is that it permits both voice and data communications using a single communications device.
Yet another technical advantage of the invention is that it permits replacement of the existing linecard in the CO with the linecard of the present invention enabling hardware changes at the CO to provide the increased bandwidth. Thus, a standard modem can be used to establish a connection with the CO and the use can still realize increased data communications.